watchdog: orion: fix compile-test dependencies

I ran into one corner case with the orion watchdog using the
atomic_io_modify interface:

drivers/watchdog/orion_wdt.o: In function `orion_stop':
orion_wdt.c:(.text.orion_stop+0x28): undefined reference to `atomic_io_modify'
drivers/watchdog/orion_wdt.o: In function `armada375_stop':
orion_wdt.c:(.text.armada375_stop+0x28): undefined reference to `atomic_io_modify'

This function is available on all 32-bit ARM builds except for ebsa110, so
we have to specifically exclude that from compile-testing.

Fixes: da2a68b3 ("watchdog: Enable COMPILE_TEST where possible")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>